Cutting elements containing a cutting layer of ultra hard materials are known in the art. Such cutting elements can be used in a number of different applications, such as tools for mining, cutting, machining and construction applications. Suitably, such cutting elements can be used in drill bits such as roller cone drill bits, percussion or hammer bits, diamond impregnation bits, and shear cutter bits.
Rotary drill bits with no moving elements are typically referred to as “drag” bits. Drag bits are often used to drill a variety of rock formations. Drag bits include those having cutting elements (sometimes referred to as cutters, cutter elements, or inserts) attached to the bit body. Cutting elements, such as shear cutters for rock bits, typically have a substrate (or body) with a cutting layer (sometimes referred to as a “cutting table” or “table”) deposited onto or otherwise bonded to the substrate at an interface surface. The substrate is generally made from cemented or sintered metal carbide, typically tungsten carbide, while the cutting layer is made from an ultra hard material such as polycrystalline diamond (PCD) or polycrystalline cubic boron nitride (PCBN).
An example of a typical drag bit having a plurality of cutting elements with ultra hard working surfaces is shown in FIG. 1. The drill bit 10 includes a bit body 12 and a plurality of blades 14 that are formed on the bit body 12. The blades 14 are separated by channels or gaps 16 that enable drilling fluid to flow between to both clean and cool the blades 14 and the cutting elements 18. Cutting elements 18 are held in the blades 14 at predetermined angular orientations and radial locations to present working surfaces 20 with a desired back rake angle against a formation to be drilled. Typically, the working surfaces 20 are generally perpendicular to the axis 19 and side surface 21 of a cylinder cutting element 18. Thus, the working surface 20 and the side surface 21 meet or intersect to form a circumferential cutting edge 22.
Nozzles 23 are typically formed in the drill bit body 12 and positioned in the gaps 16 so that fluid can be pumped to discharge drilling fluid in selected directions and at selected rates of flow between the cutting blades 14 for lubricating and cooling the drill bit 10, the blades 14, and the cutting elements 18. The drilling fluid also cleans and removes the cuttings as the drill bit rotates and penetrates the geological formation. The gaps 16, which may be referred to as “fluid courses,” are positioned to provide additional flow channels for drilling fluid and to provide a passage for formation cuttings to travel past the drill bit 10 toward the surface of a wellbore (not shown).
The drill bit 10 includes a shank 24 and a crown 26. Shank 24 is typically formed of steel or a matrix material and includes a threaded pin 28 for attachment to a drill string. Crown 26 has a cutting face 30 and outer side (gage) surface 32. The drill bit 10 also has a heel surface 45 located adjacent the outer side surface 32. The gage surface 32 and heel surface 45 may include cutting elements positioned therein to help maintain the gage of the well bore or to back ream the formation as the drill bit is removed from the well bore. The particular materials used to form drill bit bodies are selected to provide adequate toughness, while providing good resistance to abrasive and erosive wear. For example, in the case where an ultra hard cutting element is to be used, the bit body 12 may be made from powdered tungsten carbide infiltrated with a binder alloy within a suitable mold form. In one manufacturing process, the crown 26 includes a plurality of holes or pockets 34 that are sized and shaped to receive a corresponding plurality of cutting elements 18.
The combined plurality of surfaces 20 of the cutting elements 18 effectively forms the cutting face of the drill bit 10. Once the crown 26 is formed, the cutting elements 18 are positioned in the pockets 34 and affixed by any suitable method, such as by brazing, adhesion, mechanical means such as interference fit or the like. The design depicted provides the pockets 34 inclined with respect to the surface of the crown 26. The pockets 34 are inclined such that the cutting elements 18 are oriented with the working surface 20 at a desired rake angle in the direction of rotation of the bit 10, so as to enhance cutting. It should be understood that in an alternative construction (not shown), the cutting elements may each be substantially perpendicular to the surface of the crown, while an ultra hard surface is affixed to a substrate at an angle so that a desired rake angle is achieved at the working surface.
A cutting element 18 is shown in FIG. 2. A shear cutter cutting element 18 has a cylindrical cemented carbide substrate body 38 having an end face or upper surface 54. A cutting layer 44 of an ultra hard material, such as polycrystalline diamond (PCD) or polycrystalline cubic boron nitride (PCBN), forms the working surface 20 and the cutting edge 22. A bottom surface 52, referred to herein as the “interface surface”, of the cutting layer 44 is bonded onto the surface of the substrate 38. The top exposed surface or working surface 20 of the cutting layer 44 is opposite the bottom interface surface 52. The cutting layer 44 typically has a flat or planar working surface 20, but may also have a curved exposed surface, that meets the side surface 21 at a cutting edge 22.
One type of ultra hard working surface 20 for drag bits is formed from polycrystalline diamond, typically known as a polycrystalline diamond compact (PDC), PDC cutters, PDC cutting elements, or PDC inserts. Drill bits made using polycrystalline diamond compact (PDC) cutting elements are known generally as PDC bits.
FIG. 3 illustrates a cutting element in the form of an insert 76, such as a diamond enhanced insert (DEI), used in wear or cutting applications in a roller cone drill bit or percussion or hammer drill bit. Such inserts 76 can be formed from blanks comprising a substrate portion 78 formed from one or more substrate materials 80 and a cutting layer 82 having a working surface 84 formed from an ultra hard material. FIG. 4 illustrates a cutting element in the form of an insert (button or stud) with a cutting layer in the form of a cutting table used in wear or cutting applications. Such cutting elements 102 can also be formed from blanks comprising a substrate portion 104 formed from one or more substrate materials 106 and a cutting layer 108 having a working surface 110 formed from an ultra hard material. The cutting layer of such cutting elements may have chamfered edges 112.
Rotary drill bits with moving elements also utilize cutting elements containing a cutting layer of ultra hard materials. FIG. 5 illustrates a roller cone drill bit in the form of a rock bit 86 comprising a number of wear or cutting inserts 76, as discussed above and illustrated in FIG. 3. The rock bit 86 comprises a bit body having three legs 90 and a roller cutter cone 92 mounted on a lower end of each leg. The inserts 76 are provided on the surfaces of each cutter cone 92 for bearing on a rock formation being drilled. The roller cone drill bit may also contain inserts 102 (not shown), as discussed above and illustrated in FIG. 4, in areas subject to wear such as the bit leg.
FIG. 6 illustrates the inserts 76 described above as used with a percussion or hammer bit 94. The hammer bit comprises a hollow steel bit body 96 having a threaded pin 98 on an end of the body for assembling the bit onto a drill string (not shown) for drilling oil wells and the like. A plurality of the inserts 76, as discussed above and illustrated in FIG. 3, are provided on the surface of a head 100 of the body 96 for bearing on the rock formation being drilled. The percussion or hammer bit may also contain inserts 102 (not shown), as discussed above and illustrated in FIG. 4, in areas subject to wear.
The ultra hard working surface, in the form of a layer (sometimes referred to as a “table”) is bonded to the substrate at an interface. The substrate may be cemented metal carbide which may, for example, be formed by sintering a mixture of stoichiometric tungsten carbide and a metal binder.
The cutting element is typically formed by placing the cemented metal carbide substrate into a container for use in a press. A mixture of diamond grains or diamond grains and catalyst material may be placed atop the substrate and treated under high pressure, high temperature conditions. In doing so, the metal binder (often cobalt) migrates from the substrate and passes through the diamond grains to promote intergrowth between the diamond grains. As a result of the migration of the metal binder, the diamond grains become bonded to each other to form the diamond layer, and the diamond layer is also bonded to the substrate.
During the manufacture of the cutting elements, there is a desire to improve infiltration of the metal binder into the ultra hard material layer at the interface to promote improved bonding of the ultra hard material layer to the substrate. Further, there is a desire to improve the flexural strength of the substrate used to manufacture the cutting element to improve the resistance to substrate fracture during the joining process of the cutting element to the drill bit and during the operation of the drill bit.